U.S. Pat. No. 5,039,217 discloses a car-to-car distance measurement system in which one of the cars comprises a pair of headlamps disposed at a predetermined distance from each other. Each headlamp comprises an optical device having a light projector which projects pulse light having a specific code toward the car in front. Furthermore, the optical device comprises a light receiver capable of receiving the light reflected from the car ahead. Disposing the light projector and the receiver in close proximity to each other allows the respective optical axes of the light projector and the receiver to be considered substantially the same. Moreover, the optical device comprises a driving apparatus for adjusting the angle of projection of the light projector on the basis of a signal from the receiver. The system further has a central processing unit which measures the angle of projection of the pulsed light from the light projector when the light receiver of each of the headlamps detects the reflected light. This allows the determination of the distance between the two cars as well as the angle between the axes of the two cars.
The fact that the prior art system uses rotatably adjustable headlamp units makes it cumbersome to implement. Moreover, as international standards do not allow rear lamps and side markers on vehicles to be adjustably mounted the prior art system does not allow a 360 degree view around the vehicle.